Process for preparing finely particled metallic nickel powder having a spheroidal form

ABSTRACT

A process is disclosed for preparing finely divided, homogeneous, metallic nickel powder with a very narrow granulometric spectrum having a spheroidal form and with a granulometric range between 0.07 and 2 microns, characterized in that a hydroalcoholic suspension of a nickel compound selected from the class consisting of the hydroxide, the formate and the acetylacetonate is treated with hydrogen at temperatures ranging from 160* to 250* C and at hydrogen partial pressures ranging from 25 to 100 atm, in the presence of one or more additives selected from the class consisting of acrylonitrile, pyridine, and complexes of zerovalent nickel.

[451 July 24, 1973 2,65l,l05 2,726,15l

PROCESS FOR PREPARING FINELY PARTICLED METALLIC NICKEL POWDER HAVING A SPHEROIDAL FORM Inventors: Franco Montino, Casale Monferrato (Alessandria); Franco Guerriere, Novara, both of Italy Assignee: Monticatini Edison S.p.A., Milan,

Italy Filed: Dec. 21, 1971 Appl. No.: 210,608

Foreign Application Priority Data Dec. 24, 1970 Italy 33530 A/70 US. Cl. 75/0.5 AA Int. Cl B22! 9/00 Field of Search 7510.5 AA

References Cited UNITED STATES PATENTS 9/1953 Neel 75/0.5 AA l2/l955 Kern 75/05 AA 2,730,441 1/1956 Crowley 75/05 AA 2,733,142 l/l956 Glenn 75/05 AA 2,807,532 9/1957 Hahn 75/0.5 AA 2,827,473 3/1958 Franklin et al 75/05 AA Primary Examiner-W. W. Stallard Attorney -Richard K. Stevens, Ellsworth I-l Mosher et al.

[57] ABSTRACT A process is disclosed for preparing finely divided, homogeneous, metallic nickel powder with a very narrow granulometric spectrum having a spheroidal form and with a granulometric range between 0.07 and 2 microns, characterized in that a hydroalcoholic suspension of a nickel compound selected from the class consisting of the hydroxide, the formate and the acetylacetonate is treated with hydrogen at temperatures ranging from 160 to 250 C and at hydrogen partial pressures ranging from 25 to 100 am, in the presence of one or more additives selected from the class consisting of acrylonitrile, pyridine, and complexes of zerovalent nickel.

7 Claims, No Drawings PROCESS FOR PREPARING FINELY PARTICLED METALLIC NICKEL POWDER HAVING A SPHEROIDAL FORM The present invention relates to a process for preparing powder of metallic nickel. More particularly, it relatesto aproxiess for preparing finely divided, homogeneous,;., metallic'nickel powder having a changeable granulometrydep'ending on the operational conditions and varying frorrt'0.07 to 2 microns and a spheroidal form. i f

Finely divided nickel powders having a spheroidal form, with a diameter between 0.1 and 2 microns, are used more and more in powder metallurgy.

Thewer'y' -fin'e nickel powders may be also used to manufacture the socalled dispersion strengthened alloys" consisting oi fine mixtures of a dispersoid (oxide,

boride, carbide). the metallic nickel body. These alloys have an excellent heat-resistance (l,000-l,300 C), higherthan that of several superalloys and competing with'the molybdenum alloys. lnthese alloys there is an optimum relation between the radius of the dis persoid'atld'th'at of the body; for instance for a radius of 0.0l'-0-.'l imicron of the dispersoid, the radius of the body should be of the order of 0.05 0.5 micron.

The finely particled nickel powders are used, moreover, either for making different types of sintered alloys (Ni, Cr, Co, Ni-W, Ni-Cu), or for makingalloys based on Fe-Ni used as magnetic materials, or for making self-lubricating porous gears, or for making electrodes for alkalinebatteries and for fuel cells.

Furthermore, very fine nickel powders are used for making porous barriers based on Ni, for the separation in gaseous phase of uranium isotopes.

It is already known to produce powdered nickel by thermal decomposition of nickel tetracarbonyl or by reduction, under pressure of H of aqueous solutions or suspensions of nickel sulphate or nickel carbonate in the presence of organic or inorganic additives. These processes involve however the drawback of producing nickel powders with diameters greater than 1 micron, together with a rather poor control over the shape, the homogeneity and the aggregation of the particles.

It is also known to prepare finely particled metallic nickel powder by pyrolysis of bis-acrylonitrile-nickel under controlled conditions. By that process it is possible to obtain pyrophoric nickel powders having a diameter 1 micron.

The object of the present invention is therefore to provide a simple and economic process for preparing very fine nickel powder having a controllable diameter, a spheroidal form and a homogeneous granulometry.

According to the present invention finely particled and homogeneous metallic nickel powder in the granulometric range between 0.07 and 2 microns with a spheroidal form and with a very narrow granulometric spectrum, is obtained by treating with hydrogen a hydro-alcoholic suspension of a nickel compound selected from the hydrate, formate and acetylacetonate, at temperatures ranging from 160 to 250 C and at hydrogen partial pressures ranging from 25 to 100 atm in the presence of one or-more'additives selected from the class consisting of acrylonitrile, pyridine and zerovalent nickel complexes.

The addition ofa few mg]! of very fine nickel powder as nucleant is preferable but not necessary.

and preferably around 200 C, the hydrogen pressure between 25 and 100 atm. The reaction is completed in a few minutes and with practically quantitative yields.

The Ni powder thus obtained is washed with water and methanol, then dried in a nitrogen stream and under vacuum. The Ni powder product may contain as impurities C from 0.1 to 1 percent and H and N from 0.05 to 0.2 percent. These impurities can be completely eliminated by heating in a hydrogen atmosphere. The powders so obtained are characterized by a very narrow granulometry spectrum: of the' granules being within a maximum difference of i 15 20% with respect to the average diameter of the granules.

The nickel compounds suitable for use in the process according to the present invention are nickel compounds such as, for instance, nickel hydroxide, and salts such as nickel formate, and nickel acetylacetonate. The nickel compound is used in concentrations between 10 and g/ 1; and preferably around 60 g/l.

Among the compounds suited to form the hydroalcoholic solution, water-soluble alcohols or glycols may be used; preferably methyl alcohol and monoethylene glycol. The mixture of alcohol-water is used in a ratio comprised between 10:1 and 1:10 the ratio alcohol/wa ter controls, under otherwise the same conditions, the diameter of the obtained particles. High ratios give products of smaller diameter.

Additives capable of giving the spheroidal form to the particles are compounds, such as acrylonitrile and pyridine, added in quantities ranging from 1 to 50 g/l. Without the addition of these additives the powder does not have a spheroidal form and is more aggregated.

The quantity of bis-acrylonitrile-nickel or of other nickel zero-valent compounds, added to obtain a control of the particle size in the range of from 0.7 0.07 microns, can vary between 1 and 50 g/l. The greater concentrations give rise to smallerdiameters.

Small quantities of NH or alkalies, such as for instance NaOH (0.1-l g/l), promote the perfect dispersion of the additive in the reaction mixture, with consequent increase of its efficiency.

In the presence of bis-acrylonitrile-nickel or of other zerovalent nickel complexes it may be not necessary to add acrylonitrile and/or pyridine in order to give the desired spheroidal form to the granules.

The most significant advantages exhibited by the process according to the present invention may be summarized as follows:

low content of impurities in the powders;

absence of pyrophoricity;

possibility of obtaining powders having different diameters within the range of from 0.07 to 2 microns, varying the reaction parameters;

almost total absence of aggregates in the powder.

The present invention will be now described still greater in detail with reference to the following examples.

EXAMPLE 1 143 g of a 33% Ni(OH) obtained by precipitation with NaOl-l of NiCl, (equal to 47 g of dry Ni(OH) and 96 g H O) were suspended in a solution of 540 cc of monoethylene glycol and 24 cc of H in order to have a glycol/water ratio equal to 4.5/1. 26 cc of acrylonitrile, 14 cc of pyridine and 50 mg of Ni powder were added thereto. The mixture thus obtained was poured into a 2-liter stainless steel autoclave provided with a blade stirrer and resistance heating. After having eliminated the air by purging with N the temperature was brought to 200 C and 50 atm of H were charged thereto. After minutes, the heating was stopped and the whole was allowed to cool at room temperature with stirring. The nickel powder thus obtained was repeatedly washed with methanol and dried in a nitrogen stream and then under vacuum. 29 g. of nickel powders are obtained. Theaverage diameter of the granules was 1.2 microns. More than 80 percent of the granules had a diameter ranging from 1 to 1.4 microns.

The following test was carried out by varying the glycol/water ratio. The test was conducted as above described, by using 47 g of Ni(OH), (32 percent) suspended in 550 cc of glycol and 10 cc of H 0 (ratio glycol/H O 5:1). 23 cc of acrylonitrile, 14 cc of pyridine and 50 mg of very fine nickel were added to the mixture. 29 g. of powders were obtained. The nickel granules thus obtained had an average diameter of 0.8 microns and a spheroidal shape. 83 percent of the granules had a diameter ranging from 0.68 to 0.92 micron.

EXAMPLE 2 143 g of Ni(Ol-D at 31.4% (equal to 45 g of dry Ni(OH and 98 cc H O) were suspended in 500 cc of ethylene glycol plus 152 cc of R 0 to obtain 750 cc of a mixture having a ratio glycol/H O 2/1. 21 cc of acrylonitrile, 9 cc of pyridine and 1.5 g of bisacrylonitrile-nickel were added thereto. Reduction, washing and drying were carried out as described in Example 1. 28 g of powders were obtained. Granules having an average diameter of 0. l 7 microns were obtained. 90 percent of the granules had a diameter ranging from 0.14 to 0.20 micron.

By operating as above described, but with the addition of 1 g of bis-acrylonitrile-nickel, spheroidal granules with an average diameter of 0.25 microns were obtained. 86 percent of the granules had a diameter ranging from 0.2 to 0.3 micron.

EXAMPLE 3 136 g of Ni(OH) at 33 percent (equal to 45 g of dry Ni(OH and 91 g of 11 0) were suspended in 240 cc of methanol and 389 cc of H 0 in order to have a ratio methanol/H O 1/2. 5.8 g of bisacrylonitrile-nickel, 15 cc of acrylonitrile, and 5 cc of pyridine were added thereto. Reduction, washing and drying were carried out as described in Example 1. g of powders were obtained. The average diameter of the granules was 0.09 microns and their shape was spheroidal. 85 percent of the granules had a diameter ranging from 0.07 to 0.11 micron.

EXAMPLE 4 40 g of Ni-actylacetonate were suspended in 720 cc of a mixture of glycol/H O having a ratio of 1:2. 1.2 g of bisacrylonitrile-nickel, 5 cc of acrylonitrile and 5 cc of pyridine were added thereto. Reduction, washing and drying were carried out as in Example 1. 9.1 g of powders were obtained. The average diameter of the granules was 0.1 microns and the shape was spheroidal.

What is claimed is:

l. A process for preparing finely divided, homogeneous, metallic nickel powder with a very narrow granulometric spectrum having a spheroidal form and with a granulometric range between 0.07 and 2 microns, characterized in that a hydroalcoholic suspension of a nickel compound selected from the class consisting of the hydroxide, the formate and the acetylacetonate is treated with hydrogen at temperatures ranging from 160 to 250 C and at hydrogen partial pressures ranging from 25 to atm, in the presence of one or more additives selected from the class consisting of acrylonitrile, pyridine and complexes of zerovalent nickel.

2. A process according to claim 1, wherein the concentration of said nickel compound is between 10 and g/l.

3. A process according to claim 1, wherein the hydroalcoholic component comprises a lower alcohol or a glycol.

4. A process according to claim 3, wherein the hydroalcoholic solution was an alcohol/water ratio by volume between 10.1 and 1:10.

5. A process according to claim 1, wherein the additive is used in a concentration ranging from 1 to 50 g/l.

6. A process according to claim 1, wherein the complex of zerovalent nickel is bis-acrylonitrile-nickel.

7. A process according to claim 1, wherein the reaction is carried out in the presence of very fine nickel powder as nucleant.

* k k =8 l 

2. A process according to claim 1, wherein the concentration of said nickel compound is between 10 and 120 g/l.
 3. A process according to claim 1, wherein the hydroalcoholic component comprises a lower alcohol or a glycol.
 4. A process according to claim 3, wherein the hydroalcoholic solution was an alcohol/water ratio by volume between 10.1 and 1:
 10. 5. A process according to claim 1, wherein the additive is used in a concentration ranging from 1 to 50 g/l.
 6. A process according to claim 1, wherein the complex of zerovalent nickel is bis-acrylonitrile-nickel.
 7. A process according to claim 1, wherein the reaction is carried out in the presence of very fine nickel powder as nucleant. 